We study normal human subjects and patients with a variety of diseases in which the intestine may play a role in the pathogenesis of the disease in question or in which the intestine may be manipulated to therapeutic advantage. Many of our experiments utilize a triple-lumen tube perfusion method for measuring water and electrolyte absorption or secretion in specified segments of the intestine. A nonabsorbable marker is used to calculate net volume changes. Examples of our research are as follows: 1) elucidation of normal absorptive mechanisms; 2) effect of polypeptide hormones on intestinal absorption or secretion; 3) evaluation of patients with chronic diarrhea of unknown etiology; 4) studies on the mechanism of osmotic and secretory diarrhea; 5) studies on the mechanisms of diarrhea in patients with irritable colon syndrome; 6) evaluation of anal sphincter dysfunction as a cause of intractable diarrhea; 7) studies to determine why diabetic patients with diarrhea often have fecal incontinence, studies to determine if hemorrhoidectomy predisposes to fecal incontinence if patients develop diarrhea, and training of patients with chronic diarrhea to prevent episodes of fecal incontinence; and 8) mechanism of calcium and magnesium absorption.